Invader in Hawai‘i, the Queensland Longhorn Beetle
The wood-boring beetle Acalolepta aesthetica, informally known as the Queensland longhorn beetle, has emerged as a problematic invasive species on the Island of Hawai‘i. Our research established that the preferred host of A. aesthetica is the kukui (Aleurites moluccanus; also called candlenut), the state tree of the Hawaiian Islands, and other preferred hosts include valued agricultural and horticultural species.
New non-native species often pose a set of common challenges: poorly defined patterns of distribution and abundance, unknown impacts, and few established methods for monitoring and control. Acalolepta aesthetica exemplifies these challenges and has increased management concerns because longhorn beetles can cause substantial economic and ecological damage.
Preferred tree hosts
The invasive A. aesthetica population is centered on the eastern side of the Island of Hawaiʻi, with populations spreading within and out of the Puna District. Larval feeding behavior damages and can kill host trees. Documented hosts include agricultural species such as cacao (Theobroma cacao) and citrus (Citrus sp.), ornamental cycads (order Cycadales), and culturally important kukui and ʻulu (Artocarpus altilis; breadfruit) trees. Documentation of hosts was conducted by the Hawaiʻi Department of Agriculture, but patterns of host tree preference were poorly known. We conducted a study of host preferences and found that kukui was the most preferred host, and cacao was the second-most preferred host, with ʻulu, citrus, and avocado (Persea americana) also being readily used.
The species’ physical impacts of host trees made visual surveys possible. Sap oozes from infestation sites, exit holes can be seen in tree trunks and large branches, and larvae push out frass, which was used to confirm the species’ identity. We surveyed kukui along roadsides and found an infestation as far north as near Honokaʻa. Genetic analyses confirmed these outlying infestations.
Threat risk to native trees
We evaluated threats posed by A. aesthetica to native trees by conducting no-choice oviposition tests in the lab. A no-choice oviposition test evaluates whether a fertile female beetle will lay an egg on a given host plant when no other host is available. Females oviposited on all tested species in no-choice trials, but larvae grown within ʻōhiʻa (Metrosideros polymorpha) and koa (Acacia koa) all died. This species therefore poses a low risk to these two species, which are foundational to Hawaiian native forests. Acalolepta aesthetica was able to complete its development within ʻōlapa (Cheirodendron trigynum), and this species could be monitored if the distribution of A. aesthetica spreads to native forests.
The wood-boring beetle Acalolepta aesthetica, informally known as the Queensland longhorn beetle, has emerged as a problematic invasive species on the Island of Hawai‘i. Our research established that the preferred host of A. aesthetica is the kukui (Aleurites moluccanus; also called candlenut), the state tree of the Hawaiian Islands, and other preferred hosts include valued agricultural and horticultural species.
New non-native species often pose a set of common challenges: poorly defined patterns of distribution and abundance, unknown impacts, and few established methods for monitoring and control. Acalolepta aesthetica exemplifies these challenges and has increased management concerns because longhorn beetles can cause substantial economic and ecological damage.
Preferred tree hosts
The invasive A. aesthetica population is centered on the eastern side of the Island of Hawaiʻi, with populations spreading within and out of the Puna District. Larval feeding behavior damages and can kill host trees. Documented hosts include agricultural species such as cacao (Theobroma cacao) and citrus (Citrus sp.), ornamental cycads (order Cycadales), and culturally important kukui and ʻulu (Artocarpus altilis; breadfruit) trees. Documentation of hosts was conducted by the Hawaiʻi Department of Agriculture, but patterns of host tree preference were poorly known. We conducted a study of host preferences and found that kukui was the most preferred host, and cacao was the second-most preferred host, with ʻulu, citrus, and avocado (Persea americana) also being readily used.
The species’ physical impacts of host trees made visual surveys possible. Sap oozes from infestation sites, exit holes can be seen in tree trunks and large branches, and larvae push out frass, which was used to confirm the species’ identity. We surveyed kukui along roadsides and found an infestation as far north as near Honokaʻa. Genetic analyses confirmed these outlying infestations.
Threat risk to native trees
We evaluated threats posed by A. aesthetica to native trees by conducting no-choice oviposition tests in the lab. A no-choice oviposition test evaluates whether a fertile female beetle will lay an egg on a given host plant when no other host is available. Females oviposited on all tested species in no-choice trials, but larvae grown within ʻōhiʻa (Metrosideros polymorpha) and koa (Acacia koa) all died. This species therefore poses a low risk to these two species, which are foundational to Hawaiian native forests. Acalolepta aesthetica was able to complete its development within ʻōlapa (Cheirodendron trigynum), and this species could be monitored if the distribution of A. aesthetica spreads to native forests.